High fluid pressures are required for the inflation of balloons used in medical procedures such as angioplasty and radial dilation of the urethra. The balloons are typically inflated for an extended period of time using a syringe filled with fluid. However, maintaining high fluid pressures for an extended period of time is difficult by simply applying manual force to a commercially available syringe.
One approach to this problem is to use a custom-made or modified syringe. All of these syringes commonly include an outer, internally threaded member and an inner, externally threaded member f or rotational advancement of the plunger in a syringe barrel.
A disadvantage of each of these custom-made or modified syringes is that they are relatively expensive to manufacture in comparison to standard, commercially available syringes. Another disadvantage is that these syringes are more complicated to use than a standard syringe. Therefore, the physician has to become skilled at operating the device. The physician's familiarity with the device is also critical for maintaining or releasing pressure when a threshold is reached. A timely release prevents bursting the balloon or overdilating tissue. Yet another disadvantage is that these custom-made syringes are fitted with pressure gauges or indicator rods that require visual monitoring by the physician during use. The physician must actuate the modified syringe while watching a pressure indicator for a threshold pressure to be obtained. When the threshold is obtained, these custom-made syringes are manually operated for permitting fluid to exit the syringe chamber, thereby decreasing the fluid pressure therein.
Another prior art device utilizes an internally threaded outer sleeve that fixedly engages the radial projections at the proximal end of a standard syringe barrel. The device includes an externally threaded plunger that attaches to the proximal end of a standard syringe plunger for longitudinal movement of the syringe plunger with respect to the pair of radial projections at the proximal barrel end. A problem with this device is that it is expensive to manufacture. From a user's perspective, the device is large, heavy, and cumbersome, and therefore difficult and inconvenient to use.
Another disadvantage of these prior art devices is that the plunger of the syringe must be disengaged from the device to fill the syringe barrel. Alternatively, these threaded devices must be rotated to withdraw the plunger from the distal end of the barrel to fill the syringe with fluid. This is particularly annoying and time consuming when the technician or physician has initially engaged the pressure device with the syringe and forgot to initiate filling of the syringe barrel with fluid.